Studies on the Adaptation of Taxus media cv. Hicksii to Natural Temperature Reduction

The adaptation of 3-year-old Taxus media cv. Hicksii leaves to natural temperature reduction was studied. The results showed that the semilethal low temperature（LT50）of Taxus media decreased increasingly with the reduction of air temperature， from -8.13 ℃（in mid November ） to -13.01 ℃（in mid January ）. The contents of osmoregulatory substances such as soluble sugar, soluble protein and free proline increased to the the different degree, but the content of starch decreased. The contents of endogenetic hormones such as ABA rose continuously and negatively correlated to LT50 (the coefficient of correlation was -0.971 06). On the contrary， the contents of ZRs, GA1/3 and IAA reduced ，which the content of ZRs was positively correlated to LT50 (the coefficient of correlation was 0.949 72). In summary, the adaptive changes of these substances including osmoregulatory substances and endogenetic hormones of leaves of Taxus media cv. Hicksii led to the reduction of LT50, thus make Taxus media cv. Hicksii suit the low temperature condition cuitivated in Chongqing and pass the winter safely.